Photochemically reactive functional groups (“photoreactive groups” or “photogroups”) are functional groups that, when exposed to an appropriate energy source, undergo a transformation from an inactive state (i.e., ground state) to a reactive intermediate capable of forming covalent bonds with appropriate materials. Photoreactive groups can be used, for instance, to derivatize a target molecule (e.g., thermochemically), in order to then photochemically attach the derivatized target molecule to a surface. Photoreactive groups can also be used as photoinitiators for polymerization reactions.